When pumping fluids with high vapor pressure, particularly refrigerants in Organic Rankine Cycles and refrigeration cycles, CIG (Crescent Internal Gear) pumps can have issues with cavitation caused by insufficient inlet pressure. In order to meet pumping performance requirements these CIG pumps are often limited in speed or the height of fluid the CIG pump can lift. One solution is to boost the inlet pressure to the CIG pump so that it can operate without cavitation. Commonly, the entire system has to be designed around the position of the CIG pump to protect against such cavitation conditions. Often it is required that a second standalone pump be mounted low in the system to provide a low pressure boost to the CIG pump inlet.
Sealing refrigerants against escape to the surroundings is a key environmental and operational concern. Traditional mechanical seals and lip seals often are unreliable given the small amount of leakage that is allowed by governing agencies. A common solution to such sealing issues is to use a magnetic drive, which eliminates the need for a seal between the drive shaft and the pump casing. Magnetic drives operating at high speeds, however, come with another disadvantage, namely heat. Heat is generated when using magnetic drives, and as this heat builds the drive becomes less efficient. In some cases the heat generated by the drive offsets the advantage of the drive and can cause it to fail.
In addition, when pumps are used to boost inlet pressure to a CIG pump, the boost pumps are provided as completely separate pump systems, including piping/tubing, fittings and the like. Further, where boost pumps are employed it is important to ensure that sufficient inlet pressure is provided to the boost pump to prevent cavitation and damage to the boost pump.
If a separate boost pump is not employed then the system must be designed so that the CIG pump is located at the lowest point in the system in order to maximize inlet pressure. Often this is not enough, rendering the CIG pump insufficient for the application.